We will examine the effect of x-rays on cultured human mammary epithelial cells using three different research disciplines - cell biology, radiation biology and polycyclic aromatic hydrocarbon metabolism. Utilizing a system that we have recently developed for culturing human mammary epithelial cells we will develop a transformation assay. To do this, we will determine what properties correlate with mammary cell malignancy by comparing tumor and normal cells for various properties associated with malignancy in model systems and for properties known to distinguish tumor and normal mammary cells in vivo. We will measure the toxicity of mammary epithelial cells to x-rays and then, using the most relevant assay determined from the above studies, attempt to transform the cells at various sublethal x-ray doses. We will examine the cocarcinogenic synergism between x-rays and benzo(a)pyrene (BaP) metabolism by comparing the effect of low x-ray doses on BaP induced toxicity, formation and repair of BaP adducts to DNA and extent of water soluble BaP conjugate formation.